1. Field of the Invention
This invention relates to axial flow turbines and more particularly to a probe for determining Mach number at any point along the radial length of the blades used in an axial flow elastic fluid turbine.
2. Description of the Prior Art
In axial flow turbines the usual method for determining individual blade row efficiencies is to conduct pressure traverses at the inlet and exit of the blade row in question. Highly supersonic elastic fluid flow often occurs at the exit of certain blade rows situated near the low pressure end of the turbine. It has been common practice to use a truncated cone probe to conduct pressure traverses upstream and downstream from blade rows which are candidates for such supersonic flow. Results obtained from the truncated cone probe traverses for supersonic fluid flow required correction due to the effect of shock waves on the probe. The correction was based on theory, but effects such as probe blockage were seldom accounted for and thus caused the corrected results to be questionable.
U.S. Pat. No. 3,832,903 which was patented on Sept. 3, 1974, discloses a probe and method for measuring stagnation pressure for gas streams of supersonic velocity. The aforementioned prior art probe utilizes three pressure taps to indicate the relative position of the probe and detect deviations from the original orientation of the probe in the plane of deflection of the gas stream. A primary disadvantage of the prior art device is a lack of any means for determining the static pressure corresponding to the measured stagnation pressure. An additional disadvantage of the prior art includes the complexity which is introduced in its use of three pressure measuring devices and taps associated therewith for determining, through comparative pressure ratios, the proper orientation of the probe relative to the gas stream. The prior art probe is typically used in wind tunnels which have static pressure taps at their walls and thus permit Mach number determination for gas streams flowing within the wind tunnel. As such, the prior art probe is not suitable for determining static pressure at points along the radial length of axial flow turbine blades since the static pressure typically varies from the blade's platform to its tip.